Lots of man pages.

man/man3/getenv.3

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+.TH GETENV 3
+.SH NAME
+getenv, putenv \- access environment variables
+.SH SYNOPSIS
+.B #include <u.h>
+.br
+.B #include <libc.h>
+.PP
+.nf
+.B
+char* getenv(char *name)
+.br
+.B
+int   putenv(char *name, char *val)
+.fi
+.SH DESCRIPTION
+.I Getenv
+reads the contents of
+.BI /env/ name
+(see
+.IR env (3))
+into memory allocated with
+.IR malloc (2),
+0-terminates it,
+and returns a pointer to that area.
+If no file exists, 0
+is returned.
+.PP
+.I Putenv
+creates the file
+.BI /env/ name
+and writes the string
+.I val
+to it.  The terminating
+.B 0
+is not written.
+If the file value cannot be written, \-1 is returned.
+.SH SOURCE
+.B /sys/src/libc/9sys
+.SH SEE ALSO
+.IR env (3)
+.SH DIAGNOSTICS
+Sets
+.IR errstr .